The present invention relates generally to methods for sampling a halosilane source, and determining the amount of certain metal analytes present in the source. More particularly, it concerns methods for sampling a trichlorosilane supply used for manufacturing polysilicon, and determining the amount of certain metal dopants present in the sample.
Certain highly reactive compounds, such as boron trifluoride, hydrogen chloride, and trichlorosilane, among others, are reagents that can be used in semiconductor fabrication processes. In the presence of oxygen and/or water, certain such highly reactive compounds can cause the metal of storage canisters (e.g., cylinders) and/or supply lines in the fabrication system to corrode. The introduction of air and/or water into the fabrication system can be due to leaks, cylinder change-outs, exhaustion of a purifier's capacity, and/or human error. Thus, the corrosivity of such compounds dictates careful materials selection and handling methods for the delivery lines between the gas supply and the point of use.
Certain chlorosilane and fluorosilane gases can be used in the processing of certain workpieces, such as semiconductor wafers. One such chlorosilane, trichlorosilane, is a corrosive, liquefied gas that is used in large volumes in the manufacture of semiconductor-grade silicon, and in the chemical vapor deposition (CVD) of epitaxial silicon. In a fab, trichlorosilane is delivered to the tool either as a pressurized liquid, or diluted in a carrier gas, such as hydrogen. Since trichlorosilane can be the starting ingredient for wafers, metal impurities present in a trichlorosilane supply may be incorporated into the finished wafer, significantly altering the electrical characteristics of the wafer.
When metal contamination is detected in a product silicon wafer, it can be difficult to determine its origin (e.g., in reactive gas lines or a source cylinder) in the silicon wafer production system. Without being able to efficiently pinpoint the origin of a metal contamination in a polysilicon production system, it may become necessary to replace a gas cylinder, or change out components or whole sections of gas delivery hardware in order to eliminate the contamination. Furthermore, in order to determine that the contamination has been eliminated, time-consuming and costly test wafer production and analysis may be required. A relatively safe, flexible, and more accurate method for collecting a chlorosilane or fluorosilane sample at various points within a silicon wafer production system in order to isolate a contamination source is desirable.